In conventional predictive maintenance or condition based maintenance of a wind turbine component, the component operational condition is being monitored. If, in the monitoring process, a clear degradation in the component performance has been found and the deterioration has been over a given threshold, an action is triggered that the maintenance will be carried out. This usually relies on a monitoring system to detect such changes. The parameters in monitoring are usually the ones that reflect vibration, temperature, acoustic or pressure but not limited to these parameters.